/Engine/Source/Runtime/Core/Public/Containers/DiscardableKeyValueCache.h
Checks for the entry in our current map, and if not found the backfill. If the entry is in the backfill it is moved to the current map so it will not be discarded when DiscardUnusedEntries is called
bool InternalFindWhileLocked ( const KeyType & Key, ValueType & OutType, uint32 InCurrentLockFlags, uint32 & OutFlags )